CONSTITUTIVE MODELLING OF COMPACTED CLAYS FOR APPLICATIONS IN NUCLEAR WASTE DISPOSAL.

Compacted highly expansive unsaturated clays are envisaged to be employed as buffers for the long-term storage of nuclear waste in deep geological repositories. The numerical modelling of such materials is challenging. A new constitutive model for compacted clays is proposed. It accounts for the double-porosity structure, as it considers two levels of structure: the macro-structure and the micro-structure. The overall behaviour of the material is characterised as an interaction of these two levels, which are assumed to be elastoplastic and not independent. The performance of the new model in the prediction of soil behaviour is assessed and it is shown that the double structure is essential to capture the observed volumetric behaviour of compacted clays.
A numerical investigation of the behaviour upon wetting of compacted clays is conducted at both the laboratory scale and the field scale. In the former case, a swelling pressure test is studied in order to verify that the new double structure model correctly reproduces the fundamental features of the swelling behaviour. In the latter case, a large scale deep geological repository is reproduced in order to assess the predictive capabilities of the model for the long-term state of the buffer.